On Fri, May 06, 2022 at 12:07:13PM -0700, Mike Kravetz wrote:

On 5/3/22 03:03, Gerald Schaefer wrote:

quoted

On Tue, 3 May 2022 10:19:46 +0800
Baolin Wang [off-list ref] wrote:

quoted

On 5/2/2022 10:02 PM, Gerald Schaefer wrote:

[...]

quoted

quoted

Please see previous code, we'll use the original pte value to check if 
it is uffd-wp armed, and if need to mark it dirty though the hugetlbfs 
is set noop_dirty_folio().

pte_install_uffd_wp_if_needed(vma, address, pvmw.pte, pteval);

Uh, ok, that wouldn't work on s390, but we also don't have
CONFIG_PTE_MARKER_UFFD_WP / HAVE_ARCH_USERFAULTFD_WP set, so
I guess we will be fine (for now).

Still, I find it a bit unsettling that pte_install_uffd_wp_if_needed()
would work on a potential hugetlb *pte, directly de-referencing it
instead of using huge_ptep_get().

The !pte_none(*pte) check at the beginning would be broken in the
hugetlb case for s390 (not sure about other archs, but I think s390
might be the only exception strictly requiring huge_ptep_get()
for de-referencing hugetlb *pte pointers).

We could have used is_vm_hugetlb_page(vma) within the helper so as to
properly use either generic pte or hugetlb version of pte fetching.  We may
want to conditionally do set_[huge_]pte_at() too at the end.

I could prepare a patch for that even if it's not really anything urgently
needed. I assume that won't need to block this patchset since we need the
pteval for pte_dirty() check anyway and uffd-wp definitely needs it too.

Thanks,

-- 
Peter Xu